Graduation rates among the state’s public high schools decreased an average of 9 percentage points in 2011 compared with the previous year, according to statistics released today by the state Department of Education.

The drop comes in the wake of a new, federally mandated methodology for calculating the rates which state officials say is more “honest.”

“The new 2011 graduation rate presents us with a more accurate picture of the true level of high school completion across the state and we encourage all districts to study the data carefully to target their investments,” acting Education Commissioner Christopher Cerf said in a statement.

At Millburn Senior High School, the percentage of students earning diplomas dropped by 1 percentage point, while the rate at Woodbridge High School fell by 5 percentage points.

Elsewhere, the rate fell by 16 percentage points at Dover High School in Morris County, by 14 percentage points at Franklin High School in Somerset County and by nearly 7 percentage points at Cranford High School.

Until last year, schools calculated their graduation rates by dividing the number of seniors receiving diplomas by the number of seniors who enrolled at the start of the school year plus the number who had dropped out since that class entered high school.

Because the state relied on districts to self-report their graduation rates, some school systems under-reported their dropout statistics, said Justin Barra, a spokesman for the Department of Education.

The old methodology, which the department called “flawed,” also failed to account for student mobility, Barra said. Now, schools will be required to track students using a statewide data collection system that accounts for students who leave a district.

With the new calculating system in place, the percentage of students who graduated from high schools across the state dropped from 94.7 percent in 2010 to 83 percent in 2011, according to the Department of Education.

In West Orange, where the graduation rate fell by nearly 12 percentage points, Superintendent Anthony Cavanna said he prefers the new system because it will allow the district to target specific groups of students that are struggling and dropping out.

“The new system tracks students from the time they enter high school to the time they graduate. If students are not graduating, it gives us an opportunity to focus in and develop programs tailored to them,” Cavanna said.

“This is a good snapshot of where we really are,” he said. “Yes, our rate decreased, but so did the whole state.”

The new statistics also revealed some oddities.

Star-Ledger fileNewark's Central High School 2011 graduation is pictured above. The federal government has developed a more accurate measure of graduation rates, which New Jersey is now implementing.

The percentage of students graduating from Cumberland County’s Memorial High School fell from 86 percent to 14 percent while Lakewood High School’s rate increased by nearly 33 percentage points. The report did not offer any explanation for the huge changes.

Of the more than 75 districts that reported perfect graduation rates in 2010, just seven maintained them under the new methodology for 2011.

The seven are: Leap Academy University Charter School in Camden; the Academy for Math, Science and Engineering High School in Morris County; the Marine Academy of Technology and Environmental Sciences in Ocean County; and four vocational high schools in Monmouth County.

Though many districts alerted parents that the new methodology would change graduation rates, some parents may still take issue with the declines, said Lynne Strickland, executive director of the Garden State Coalition of Schools.

“Districts will need to provide parents adequate backup and explanation for these shifts if they have not done so already,” Strickland said. “There’s always a chance some parents will be surprised or angry.”

The new graduation rates for individual high schools come one day after the Christie administration unveiled plans to increase graduation standards by requiring high school students to take new end-of-year tests in as many as four subjects. The tests will become a requirement for graduation.

Cerf said the new exams and the new graduation rate methodology together will strengthen the value of a New Jersey high school diploma.

“We should approach these results with both confidence and humility,” he said in a statement. “We are taking a crucial step not only to increase the number of high school graduates, but to make a New Jersey diploma the gold standard for the country.”